1. Field of the Invention
The present invention relates to a catalyst container which is used for containing therein catalysts for purifying exhaust gases from an internal combustion engine. In particular, it relates to a simpler construction of the catalyst container itself as well as to a catalyst container with a heat shield cover. The heat shield cover is to prevent the damages to the surroundings such as the road surface or the like by the heat which is radiated from the bottom surface on the downstream side of the catalyst container.
2. Description of the Related Art
As this kind of catalyst container itself, there is known the following, e.g., in Japanese Published Unexamined Patent Application No. 1428/1988. Namely, the catalyst container is normally made up of a cylindrical member for containing therein catalysts, and coned connection members which are connected to both ends, as seen in the axial direction, of the cylindrical member and which are respectively tapered so as to become smaller in diameter in a direction away from the cylindrical member. This cylindrical member is made up of two longitudinally segmented halves (i.e., segmented in the axial direction). A substrate or a catalyst support block is sandwitched inside these two segmented halves. The segmented halves are thereafter welded together at flanges which are provided along the divided surfaces of the halves to thereby integrally assemble the constituent members together. The catalyst container of this kind of construction has the following disadvantages. Namely, a metallic mold for forming the segmented halves becomes large in size. Further, there are required additional members for aligning the substrate relative to the catalyst container itself, as well as members for hermetically sealing the catalyst container, resulting in a higher cost.
Aside from the above-described conventional catalyst container itself, there is also known the following in U.S. Pat. No. 4,070,158 in which tapered members are welded together. Namely, as shown in FIGS. 12A and 12B, a casing xe2x80x9caxe2x80x9d of this catalyst container is made up of a cylindrical portion b and coned portions c, c. A catalyst carrier body d around which is rolled a ceramic fiber mat (sealing mat) e is contained or accommodated inside the cylindrical portion b. The cylindrical portion b is formed of a plate member such that the inner diameter becomes smaller than D, as illustrated in FIG. 12B, with an allowance b1 for overlapping the circumferential both ends. In assembling, the inner diameter of the cylindrical portion b is forcibly expanded against the elastic force to thereby insert thereinto the catalyst carrier body d around which is rolled the sealing mat e. The forcibly expanded cylindrical portion b is then allowed to become free to thereby cause the tightening force due to the restoring force of the cylindrical portion b to operate. In this state the axially extending overlapped end portion b2 of the rolled cylindrical portion b is then welded. Thereafter, the large diameter portion C1 of each of the coned or tapered portions C is inserted into the cylindrical portion b. In this manner, the cylindrical portion b and the end portion of each of the sealing mats e are held together in position by means of an inwardly bent collar C2 which is formed in the large diameter end of the tapered portion C. The cylindrical portion b and the tapered portion C are then welded together at a circumferentially extending welding portion C3.
It is possible with this casing xe2x80x9caxe2x80x9d to hold the catalyst carrier body d in a hermetically sealed manner. However, since the inner diameter D cannot always be made constant to a certain fixed dimension, there is a possibility that a clearance occurs between the large diameter portion C1 and the cylindrical portion b, or conversely that the large diameter portion C1 is too large to be inserted into the cylindrical portion b depending on the relative sizes of both portions b, C1. Further, the machining work of drawing the inwardly bent collar C2 is not easy.
As the catalyst container with a heat shield cover in order to prevent the heat radiation from the bottom surface of the catalyst container to the surroundings such as onto the road surface, or the like, it is normal practice to mount the heat shield cover by means of welding or caulking to the container case of the catalyst container. If this kind of mounting arrangement is employed, it is impossible to replace only the cover and, consequently, the cover must be replaced together with the catalyst carrier itself. Further, there is also known one in which the heat shield cover is mounted by means of bolts and nuts (e.g., in Japanese Published Examined Utility Model Registration Application No. 26008/1982). If an arrangement is made, like the above embodiment, that the entire bottom surface is covered with the heat shield cover, the heat shield cover becomes large in size, and a large number of fixing parts such as bolts, nuts or the like must be used. As a result, the costs for parts and for assembling become higher. Further, in recent catalyst containers, the catalyst carriers are often wrapped with sealing mats which have thermally insulating characteristics. In the catalyst containers of this kind of construction, there is no need of covering also that part of the catalyst carrier which is wrapped with the sealing mat.
In view of the above points, the present invention has an object of providing a catalyst container in which the forming and welding of the coned portion are easy. It is another object of the present invention to provide a catalyst container in which the heat shield cover is light in weight and small in size and the cover alone can be replaced, and in which a special member is not required for mounting the heat shield cover on the catalyst container.
In order to attain the above and other objects, according to a first aspect of the present invention, there is provided a catalyst container comprising: a columnar porous catalyst carrier; a sealing mat surrounding an outer circumferential surface of the catalyst carrier; a cylindrical body surrounding an outer circumferential surface of the sealing mat, the cylindrical body having that overlapped portion of a rolled sheet of metal which is welded in an axial direction of the cylindrical body; a coned portion welded, at a large diameter portion thereof, to each axial end of the cylindrical body; wherein the large diameter portion of each of the coned portions has a flange which extends radially outward, and wherein each of the axial ends of the cylindrical body is in contact with an outward end surface of the flange and is fillet-welded along an outer corner which is formed by the flange and the cylindrical body.
According to this catalyst container, the flange on the large diameter portion of the coned portion extends outward. Therefore, the forming of the flange is easy. Further, as long as the inner diameter and outer diameter of the coned portion fall within the width of the flange, the assembling can be carried out. It follows that the cylindrical body can be reduced in diameter by operating a sufficient tightening force to the sealing mat. The airtightness and the positioning of the catalyst carrier can thus be made surely. The welding portion between the flange and the cylindrical body can provide a sufficient allowance for welding by subjecting the flange to fillet welding with the cylindrical body. Therefore, the welding portion can attain a large welding strength.
Preferably, each of said axial ends of the cylindrical body is aligned so as to be substantially in the center of the flange.
According to this feature, that inner diameter of the end of the coned portion which is formed by the inner circumference of the flange is smaller in diameter than the inner diameter of the cylindrical body. Therefore, the flow of the exhaust gases which enter from the coned portion into the cylindrical body can be prevented from striking the end of the sealing mat. The damages to the end of the sealing mat can thus be avoided.
According to a second aspect of the present invention, there is provided a catalyst container comprising: a casing having a cylindrical body for containing a catalyst carrier body inside the cylindrical body; a rear coned portion which extends rearward from a rear end of the casing, the rear coned portion having a first flange connected to a rear end thereof; a heat shield cover which is mounted under the casing by connecting a second flange connected to a front end of a downstream exhaust gas pipe to the first flange with bolts and nuts; wherein the heat shield cover comprises a mounting flange portion and a cover portion, the mounting flange portion being extended so as to abut with an upstream surface of a lower part of the first flange and having bolt holes which are coaxial with bolt holes of the first flange, the cover portion being bent backward and forward to cover the bottom surfaces of the rear coned portion and said first and second flanges, said heat shield cover being connected to the first and second flanges with bolts and nuts by inserting the bolts from the side of the mounting flange portion.
Preferably, the cover portion of the heat shield cover comprises: a rear cover portion which is bent from the mounting flange portion rearward to cover the bottom surfaces of the first and second flanges; an intermediate portion which is bent forward from the rear cover portion; and a front cover portion which extends further from the intermediate portion to cover the bottom surface of the rear coned portion.
According to the second aspect of the present invention, the heat shield cover can be mounted with the bolts that are used to couple the flange on the catalyst container and the flange on the exhaust gas pipe on the downstream side. Therefore, the number of parts can be reduced. In addition, only the rear coned portion and the two flanges that are heated to a high temperature by the exhaust gases are covered by the heat shield cover. Therefore, the necessary heat shielding function can be attained by a minimum number of parts.
In assembling the heat shield cover to the catalyst container, bolts are inserted from a front side of the flange through the two flanges. The bolts are respectively fitted with nuts and are tightened for fixing the heat shield cover in position. In this arrangement, since that side on the nuts is not covered with the heat shied cover, a tightening tool can be easily operated in the available space. The assembling can thus be efficiently performed.